The secretion of hypophysial anterior lobe hormone is regulated by the peripheral hormone secreted by each target organ and the secretion-promoting or secretion-suppressing hormone secreted by the hypothalamus, which is the center superior to the hypophysial anterior lobe, and this group of hormones hereinafter generically referred to as hypothalamic hormone in this specification. To date, nine hypothalamic hormones have been identified, for example, thyroid-stimulating hormone-releasing hormone (TRH), and gonadotropin releasing hormone [GnRH, also known as luteinizing hormone releasing hormone (LHRH)], etc. It is conjectured that these hypothalamic hormones exhibit their hormone actions etc. via receptors assumed to be present in the hypophysial anterior lobe, and analyses of receptor genes specific to these hormones, including humans, are ongoing. Antagonists or agonists that act specifically and selectively on these receptors would therefore regulate the action of hypothalamic hormones and hence regulate the secretion of hypophysial anterior lobe hormone. As a result, such antagonists or agonists are expected to prevent or treat diseases depending on these hypophysial anterior lobe hormone.
Known compounds possessing GnRH-antagonizing activity include GnRH-derived linear peptides (U.S. Pat. No. 5,140,009 and U.S. Pat. No. 5,171,835), a cyclic hexapeptide derivative (JP-A-61-191698), a bicyclic peptide derivative [Journal of Medicinal Chemistry, Vol. 36, pp. 3265-3273 (1993)], and so forth. Non-peptide compounds possessing GnRH-antagonizing activity include compounds described in WO 95/28405, WO 97/14697 and WO 97/14682, etc.
ZA 86/9289 describes 1,4-dihydro-1-ethyl-7-phenylpyrrolo[1,2-a]pyrimidin-4-one in Example 22.
Peptide compounds pose a large number of problems to be resolved with respect to oral absorbability, dosage form, dose volume, drug stability, sustained action, metabolic stability etc. There is strong demand for an oral GnRH antagonist, especially one based on a non-peptide compound, that has excellent therapeutic effect on hormone-dependent cancers, e.g., prostatic cancer, endometriosis, precocious puberty etc., and that does not show transient hypophysial-gonadotropic action (acute action).